•washed up over a bank 5 to 25 feet in height and rushed back 100 to 200 feet into the alder thicket, which is much farther than the waves reached in 1909. Much gravel and sand, stones a foot or two in diameter, and ice blocks (PI. CL, B) up to ten tons in weight were thrown in among the trees. Alders, 9 to 11 inches in diameter, were stripped of leaves and bark, and bent backward or broken off short, or uprooted, or buried beneath the gravel and bowlders. The river bank, which at some points of measurement was cut back from £ to 5 feet in 1909, was fairly eaten up by the iceberg waves which crossed the river in 1910, as is proved by measurements at the same points along the bank of the stream facing the glacier, where the recession of the river bank was from 40 to 60 feet.
The amount of retreat of the river bank is shown in the following tables, the 1909 measurements having been made by the railway engineers, while those of 1910 were made by our topographer from points on the same pair of short baselines which Mr. Johnson established the year before. The material of the river bank is very coarse, unconsoli-dated, glacial gravel and bowlders. The points of observation are on the eastern bank of Copper Biver, nearly opposite the middle of Childs Glacier.
MEASUREMENTS FROM BASELINES TO BANK OF COPPER RIVER. IN 1909 AND 1910
Place of Measurement July 19, 1909 Aug. 1, 1909 Oct. S3, 1909 Aug. 18, 1910
Pt. A to river bank 44 feet 41 feet In river
Pt. B " " 63 " 58 " In river
Pt. E " " 67 " 66 " 65ifeet 16 feet
Pt.F " " 64 " 49 " 45* " -15 feet
Pt. E is the only one of the points of measurements that was left in 1910, the river bank having receded beyond the sites of the other three, though in the case of Pt. F the position was determined exactly by measurement of direction and distance from Pt. E. These measurements show that the increase in iceberg discharge in the river, which was narrowed by the advance of the glacier, resulted in retreat of the river bank as follows:
AMOUNTS or RECESSION OF RIVEB BANK THROUGH CUTTING BY ICEBERG WAVES IN
1909 AND 1910
Days Between Observations Pt. A Pt. B Pt.E Pt. F
July 19 to Aug. 1, 1909, 13 days 3 feet 5 feet If oot 5 feet
Aug. 1 to Oct. 23, 83 days $ foot sift.
Oct. 23 to ------ ,* 1909,
------ 1 to Aug. 18, 1910 — days Over 41 ft. Over 58 ft. 49£ ft. 60$ ft.
In addition to the retreat at these points there was in 1910 a general retreat of the whole river bank facing the glacier, shown particularly well by the undercutting and
i Dates between which the river was closed by ice, so that wave work ceased, though there may have been some erosion of the river bank by the ice blocks which were shoved against the river during the winter.